Racsophonic amplifier hearing-aid



Jul 17, 1934.

H. LIEBER r AL KICROPHONIC AMPLIFIER HEARING AID DEVICE Original Filed July 25, 1932 2 Sheets-Sheet 1 INVENTORS H060 4 IEBER E C. N/CHOL IDES SAPMaRu ATTORNEY y 7, 1934. H. LIEBER El AL MICROPHONIC AMPLIFIER HEARING AID DEVICE.

2 Sheets-Sheet 2 Original Filed July 25. 1932 llHlHllHll ll INVENTORS SMPMh ATTORNEY HuGO'ZIEBEE E-C-N/CHOL/DES Reissued July 157, 1934 MICROPHONE) AMPLIFIER HEARING-AID DEVICE Hugo Lieber and Emmanuel Christ Nicholides,

New York, N. Y., assignors, by mesne assignments, to Lieber Patents Corporation, New York, N. Y., a corporation of New York Original No. 1,939,627, dated December 12, 1933', Serial No. 624,424, July 25, 1932. Application for reissue February 9', 1934, Serial No. 710,514

12' Claims.

This invention relates to niicrophonic amplifier hearing-aid devices, and it has among its objccts portable aid devices provided with an improved microphone' amplifier,- that is efiicient,

powerful and accurate inamplifying and repro ducing speech and sound, as well as simple in construction, and smalland inconspicuous in appearance.

The features and obiects of the invention will be best understood from the following description and explanation of an exemplification thereof, reference being had to the accompanying drawings, wherein Fig. 1 is a diagrammatic view of, a hearing-aid device embodying the invention;

of F18. 2;

Fig. Sis a partially phantom view of the arrangement of the contact plugs and sockets of the amplifier with their interior contact mem bers;

Fig. 7 is a side elevational view mounted on the battery; and

Fig. 8 is. a top horizontal view of the amplifier mounted on the battery.

Portable hearing-aid devices for hard-of-hearing persons now in general use are composed of a microphone transmitter; a receiver, and a battery connected inseries, the: sound impulses impressed on the transmitter generating electrical oscillations which then reproduce the sound in the receiver and impress it on the hearing organs. A resistor and a cutout are usually included in the circuit of the receiver to permit regulation of the sound intensity and disconnection of the battery when the device is not in use.

Users of such hearing-aid devices almost invariably demand that the device shall be inconspicuous izrwear. The receiverand the associated elements-must therefore be extremely Since the device is almost continuously used, its elements are subjected toheavy mechanicaland electrical strains. These are diflicult to meet on account of the size limits. Furthermore, since most of the usersare laymen with little mechanical or electrical knowledge, it isimportantthat 30 or! the amplifier the'instrument shall be simple, easy to manip ulate, and require a minimum of attention.

The foregoing requirements impose serious lim itations on the intensity and the clearness of the sound reproduction, and for this reason attempts have been made to provide such hearingmid de-' vices with amplifiers. Tube amplifier hearing aids found almost no use, because their excessive size made them impractical. lVIicrophone am plifiers came into a somewhatwider use, but they are still very limited, because of the deterioration of the microphoneamplification-after short use, and also because their operating limitations'were found' to render it difl'lcult to provide practical small microphone amplifier hearing-aids-in' which the improvement due to the amplification is 'stfl flcient to outweight the complications.

The present invention provides a microphone; amplifier hearing-aid that will stand long use without deterioration. is rigid and eflicient, requires little attention, anbl; is small and inconspicuous.

The general arrangement of the hearing-aid exemplifying the invention is shown diagram matically in Fig. 1. It comprises'a telephone receiver 11, a transmitter 12, a battery 1-3,'a connesting cord 14 and a microphone amplifier 15; The receivcrrtelephon'e 11 has an actuating coil 16 and is-pcreferably made very small, midget size. The receiver has two socket terminals leading from the actuating coil 16, the socket terminals being detachably engaged by contact plugs 17 of a double strand branch 18 of the connecting cord 14. Instead of atelephone receiver, a bone-conduc'tion receiver may be used which translates electric oscillations supplied from a microphone into mechanical vibrations and imparts them to the head bone structure toinduce'hea'ring in the auditory nerves. r

The transmitter 12 isshown 'com pri'sing two microphones 21-, 22, each" of which may com; prise a'carb'on block 23', a carbon diaphragm 24', and a plurality of carbon balls or granules disposed therebetween to vary the resistance between the carbon block and the diaphragm in accordance with the sound impulses impinging uponthe' diaphragm.

The transmitter has mounted thereon a control-unit 26 comprising a resistor 27-, a stationary contact member 28, a sliding contact'rod 29, and a. movable contact member 30' slidable thereon by anexternally projecting knob to be moved from the position where it is out of contact with the resistor 2'7- and the contact member 28 to positions where it, engages and makes contact between rod 29 and the contact member 28 and the resistor 27, cutting out the resistor as it moves forward.

The is further provided with three plug contacts 31, 32, 33 connected,'respectively, to the resistor 2'7, the movable contact member 30, and to the carbon block of microphone 22,. the diaphragm of this microphone being corrnected through a conductor with the diaphragm of the other microphone 21, the carbon block of which is in turn connected to the stationary contact member 28 of the controiunit:

The three plug contacts .31, 32,33 of the transmitter are engaged by three plug pins 34, 35, 36, respectively, of transmitter plug 3'7 disposed at the end of a three stranded branch 38 of the connecting cord 14.

The microphone amplifier as actually constructed and used is shown enlarged in' Figs. 2 to 6, the following description and data of its oolistrmtion and materials being given as a guide in practicing theinvention, without intention to limit the invention thereto.

The amplifier comprises a pair of angularlybent t magnets'41 of high quality steel horizontally assembled with like poles 42 of their inner arms on opposite sides of the rectangular rearpiece 430i a cmtral round core member 44 of soft iron having high permeability.

The end surfaces 45 of the outer arms of the magnets 41 abut against the rear side of a verticaily disposed, somewhatwider, flat, rectangular pole plate 46 of soft, highly permeable, iron extending'hetween the arms, making a good magnetic joint therewith. The pole plate 48 has a oaiicallyahaped, central perforation 4'7 surrounding theend of the central core, but spaced tberefrom'by an annular gap which is smallest spring members 59, formed of doubled-over reat' the ooihciding front levels of the pole plate and the coin end toreduce leakage. Slots 48 are providedin the pole plate 46 to reduce the eddy currents that are induced by flux changes.

0n the center core 44 is mountedthe inducing coil. whicwls'covered by a strip 53 of varnished i oloth"of similarinsulating material wound around-the coil tunisiand-fastened in place by posting. The strip has securedthereto, by rivetirz or otherwise, two resilient contact strips 54 and 55, of phosphor bronze, for instance; In winding the cloth strip.53 over the turns, the end portion of the strip is wound over the portions of the two contact strips underlying the cloth strln attachhig the contact strips 54 and 55 to the opposite sides of the'ooil. The two ends of the coil are then soldered to the projecting portions of the wntact-strlps 54 and 55, which form. terminal connections for the coil 49. As shown mm. 4, thecontact strip 543 bent under the spool end, establishing an electnleal'connection with the underlying portion of core 44; and l the other contact strip 55 is insulated and bent upwardly over the coil, its spring action pressing it away from the coil.

Themngnet members 41, core 44, coil 49 and .poleqilatdfl are held together as a unit by a 'strap57'ofbrasaorlikematerial, which is bent to conform to the outer contour of the asaembledcore members. The end portions of the strap'rare doubled over, to form flanges underlying the ends of the pole plate 46 and are clamped thereto by flat-head screws 58 so that all the elements-are held firmly in place. To prevent :the loosening ofany of the elements,

flient metal strips, may be inserted between the outer magnet surfaces and the strap 5'7 to hold:

all the elements under pressure. To facilitate the assembly, the center core 44 has its two rec-- tan gular bottom projections 43 secured, as by rivets 60, to the bottom portion of the clamping strap 5'7. Insulator ring 61 holds the end of core 44 spaced from the pole plate.

A thin resilient diaphragm 62 of hardened steel, or similar resilient material, in the form of a rectangular strip, is disposed in front of the pole plate 26 and has its ends clamped between adjusting blocks 63 and clamping blocks 64 to the ends'of the pole plate 46, spaced therefrom, screws 65 threaded into holes in the pole plate ends serving to hold the blocks 63 and 64 in place. This permits free vibration of the main portion of the diaphragm 62 between the inner edges of the adjusting blocks 63, the length of the vibrating diaphragm being adjustable by shifting the adjusting blocks 63 along their slots 66 toward, or away from, the center of the pole plate.

The center portion '70 of the diaphragm 62 is made somewhat wider on the sides to form a square-like member, and has secured to its rear side, as by soldering a flat, similarly-shaped armature '71 of soft magnetic iron, the armature lying with its center over the upper pole surface of the central core 44 and with its peripheral portion over the edge portion of the surrounding pole plate 46. The height of adjusting blocks 63 and the thickness of the armature are proportioned to provide a small armature gap between the armature 71 and theunderlying pole surfaces of the center core44 and the pole plate 46. The armature and the underlying pole surfaces of the center core 44 and pole plate 46 form thus two small gaps in series througlrwhich the permanent flux of the magnets 41 and the flux induced by the. coilf49passes.

. To the front side of the center portion '70 of diaphragm 62, in alignment with the underlying armatm'e '71, is secured a flat contact plate 72 of carbon by plating, spraying; painting, or otherwise covering with a metal coating the rear side of the plate and soldering, or otherwise attaching, it to'theunderlying portion of diaphragm 62' so that the armature, the carbon plate, and the intermediate diaphragm portion '70 constitute a substantially flat rigid member, having-extending from the oppesitesides thereof two resilient diaphragm strip extensions which clamped at the ends to hold the armature spaced by a small gap from the rearwardly lying magnet pole faces. The central rigid member with the two resilient strip extensions constitute thus a diaphragm unit to which the magnet core body with its inducing coil imparts a vibratory movement in the direction away and toward the pole faces of thecore.

Supported on the pole-face plate 46, and mounted directly in front of the carbon plate 72, is a microphone casing '75 made of a fiat rectangular block of insulating material, such as phenolic condensation product, forming a border wall surrounding an inner, preferably circular, flat microphone cell '76 extending in vertical direction. At the rear side, thecell has a circular opening '77 bounded by a flat rim lying adjacent the front surface of the carbon plate -72, and at the front side, the cell has a. circular opening closed by a circular contact plate or member '79,

of carbon, fitting into a depression formed around the cell opening on the front side of the block '75. At its fom' rear "corners the microphone casing block '75 has rectangular spacing projections 82 extending towarck the face of the pole plate 46 to hold the rear wall of the'cell 76 at a distance from the poleface and the rear edges of the cell 76 directly in front of the carbon plate '72 of the diaphragm unit, spaced therefrom by a small gap 83. The casing block is secured to the plate by four flat-head screws '78. The contact member 79 is-held clamped in the front depression 80 of the microphone block '75 by a metal strip having one bent-over end 86 slipped under the rear side of one edge of block 75, while the other end is fastened by a screw 87 to the opposite edge of block 75.

The interior of the cell 76 is filled with carbon grains so that, in the normal position, with the cell in vertical direction, the grains rest against the carbon plate '72 and contact member 79 under the pressure of their own weight only, as shown in Fig. 4. The gap 83 between the diaphragm carbon plate 72 and the rear edge of cell '76 is of a size at which falling out of grains from the cell during the reciprocating vibration movement of the plate is prevented, the plate decreasing the resistance of the carbon paths in the cell when moving toward it and increasing the resistance when moving away from the cell.

With the magnet cores assembled and supported on one side of the pole plate and the diaphragm unit and the microphone cell on the opposite side of the pole plate, the several elements may be readily assembled as a unit and tested in final condition.

The combined electromagnetic-microphone unit is housed in a low, narrow rectangular casing 90 of insulating material, such as a phenolic condensation product, which has an interior rectangular chamber 91 that is arranged to be closed at the front side opening by a'flat cover 92 fitting between two ledges projecting from the bottom wall 93 and top wall 94. The rear portions of the bottom and top walls are of extra thickness to fit the bottom and top surfaces of the magnet assembly, the front portions of the walls being thinner to accommodate the somewhat wider pole plate 46 and microphone casing '75 mounted thereon. The right end wall 96 of the casing is also of increased thickness and has horizontally imbedded therein, as by molding, three socket sleeves 9'7, 98, 99 arranged to be engaged by three plug pins 101 to 103 of a plug 104 at the end of cord 14 from the receiver 11 and transmitter 12. The rear ends of the socket sleeves 97 to 99 end flush at the interior side of end wall 96.

The inner end of sleeve 97 has riveted thereto a connector strip 105 going upwardly along the end wall 96, then (as shown in dotted lines) running inwardly on the under side of the top wall 94, and terminating in a spring above the contact strip 55 of the inducing coil, making contact therewith.

The inner end of sleeve 98 has riveted thereto a connector strip 106 going downwardly along the end wall, and then .rearward'ly along the bottom wall to make contact with an anchor block 107 to which one battery plug 108 mounted on the bottom wall 93 of the casing is secured, making thus a direct bypass connection between socket sleeve 102 and battery plug 108.

The inner end of sleeve 99 has riveted thereto a connector strip 109 going first forwardly along the end wall 96, then bending and running underneath the front cover 92, and terminating in a spring unit 110 which is held by the cover 92 pressed against the metal strip 85 holding contact member 79 and making thus connection with one terminal of the microphone cell '16. The connector strip 109 may be readily bent, away in front, or back in place, to. permit inserting or removal of the electromagnetic microphone unit.

There is an additional battery plug pin 111 mounted on the under side will 92 of the casing, the inner pin end having secured thereto by a block 112 a contact strip 114'going to the rear wall and terminating in a spring contact member making contact with the rear of the holder strap 57 and therethrough with the diaphragm carbon plate 72 of the microphone cell, and with the grounding contact 54 of the actuating coil 49.

Upon insertion of the assembled electromagnetic-microphone unit in the casing and closing the cover, contacts are automatically established between contact sleeve 97' and coil contact 55; betweencontact sleeve 99 and microphone cell plate 79; between battery plug 111 and the common contact of the carbon plate '72 of the cell and the grounded end of coil 55; there being also provided the bypass connection between the second battery' plug 108 and contact sleeve 98. In order to'firmly hold the electromagnetic-microphone unit in place, the four corners of the pole plate are fastened to the underlying wall projections by screws 116. The cover is fastened in place with screwsli'l at its four corners.

To operate the hearing-aid device with the microphone amplifier, the cord plugs 1'7, 37, 104 are plugged in to the receiver 11, transmitter 12 and amplifier 15, and the amplifier 'is plugged in into the battery 13, establishing the circuits as shown in Fig. 1. To set the device in operation, the sliding contact member is moved into energizing position and the amounts of resistance 27 adjusted to fit the requirements.

In order to enable ready practice of the invention, but without limiting it thereto, there are given below the actual construction data of the microphone amplifier described above:

The permanent magnets 41 are of 17% cobalt steel, and have an area of about .288 square centimeters and a length of 1.4 centimeters. The center core 42 is of an iron-nickel alloy of high permeability, is 1.15 centimeters long-and has a diameter of .32 centimeters. The diaphragm 62 is of hardened steel .010" thick, and the active part between the inner edges of the adjusting blocks 53 is 2.25 centimeters long and .7 centimeters wide; its center portion T0 is 1.05 centimeters long and 1.05 centimeters wide; and its central equivalent mass in vibration is about .14 grams. The armature '71 is'of cold rolled steel, .015" thick, 1.0 centimeters long, .9 centimeters wide, and its mass is .32 grams. The carbon plate '12 is of highly compressed carbon, .020" thick, 1.05 centimeters long, 1.05 centimeters wide, and its mass is .085 grams. The total effective vibratory mass of the diaphragm unit including the diaphragm 62, the armature 71, balls, and the carbon plate 72 is .67 grams;

and the stillness S of the diaphragm unit against lateral displacement is about 85.510 vdynes per centimeter. The natural frequency of the diaphragm unit is about 1800, cycles per second. The actuating coil has 800 turns of No. 39 copper wire and its impedance is 50 ohms at about 200 cycles alternating current of 2 milliamperes. The armature covers an effective area of .073 square centimeters on the core pole and .45 square centimeters on the pole plate. The two gaps have a length of about 3 to 4 mils when the armature is under the action ot the permanent magnetic field. 'Ihe microphone cell lass a diameter of B" and a thickness of which together with the gapto the carbon plate gives a thickness of 'i8'mils; The cell is filled with carbon balls 0.5 millimeters in diameter. The maximum gap between the carbon plate and the rear edge of the cell is .25 millimeters. The total number of carbon balls in a filling is about 900. The assembled mechanism, without the casing, is 3 centimeters long, 1.6 centimeters high, and 1.6 centimeters deep. The mechanism with the casing is. 4.5 centimeters long, 1.9 centimeters high, 2.2 centimeters deep, and its total weight-is 38 grams. The microphone cord plug 104 is 1.4 centimeters long, .8 centimeters high, and. centimeters deep.

When the microphone transmitter 12 is not actuated, and no oscillatory currents flow through the actuating coil 49, only a permanent fluxis induced in the armature gaps of the amplifier 15, the flux passing from the inner poles 42 of magnets 41, through center core 42 to its upper pole face, then through the short inner gap into the armature 71, then through the armatm'e and short outer gap into the pole face of pole plate 46, and therethrough to the outer poles 450! the magnets 41 of opposite polarity. Uhder the action of this permanent flux, the diaphragm 62 with the armature '71 will be held deflected toward the pole plate reducing the gap thereto. 1 If sound waves impinge upon the microphone transmitter 12, making it produce oscillatory sound currents, corresponding oscillatory fluxes are lnduced in the magnet coresystem. these oscilia'tory'fiuxes being superposed on the permanent mm and causing it to increase and decrease in accordance with the current oscillations. The resulting flux fluctuations vary the attraction exthe erasedon-the armature '11 and cause the diaphragm to vibrate in accordance with the flux oscillations:- vibratory action 01 the diaphragmoi imparts a correspondingaeciprocatto'the carbon plate '12 causing it to pressure on the carbon in the cell and correspondingly vary the resistance-urine carbon; ball paths in acc rdance with the 801111110801111316118., The resistance variatioris :set up amplified current variation in the receiver circuit connected in series with the mi- 'crophone carbon balls and the battery. -pr ducing amplified soimd impulses in the receiver.

The microphone amplified hearing-aid described above, and its special microphone ampliiierembody features of construction and relationship which make the amplifying action stable and free from deterioration in use; assure uniformity of response and a high degree of intensity as well as quality of reproduction over the entire range sound frequency important for hard-of-hearhig' persons; and enable reduction of the size and "shaping of the structure of the hearing-aids in a .way to render them convenient and inconspicuou s.

The microphone chamber and the vibrating diaphragm unit cooperating therewith are of special construction. In the past, either relatively large carbon balls or veryfine formless grains were preferably used as microphone chamber fillings. .In accordance. with the, present invention,

the chamber or cell filling is preferably made of I very small carbonballs, for instance, of 0.5 millimeter diameter, generally available in the trade,

.11 satisfactory. results are also obtained with balls of other sizes not larger than about 0.7 millimeter. r

The cell for holding the carbon balls is of generally symmetrical, flat shape, and dimensioned to hold about 3 to 5 balls in series between; the rear and front contact walls. The ratio of the thickn'essof the cell to the area thereof should be between about 1:25 and 1:50. Thus, with a chamber" having a thickness of about '15 mils, a diameter of it", and a filling of carbon balls of 0.5 millimeter, very good results are obtained.

At the front side of the chamber the carbon balls rest against, and make contact with, a terminal plate of carbon secured over the front opening of: the chamber. At the opposite side of the chamber, in front of the magnet, the carbon balls rest against, and make contact with, a carbon plate somewhat larger than the rear opening and held spaced by a gap therefrom to prevent falling out of the balls, but yet permit to push the balls slightly into the interior of the chamber or release themtherefrom in accordance with the oscillatory reciprocating movement impart- :griio the plate by the diaphragm of which it is a An essential condition for good amplifiermicrpphone action is the use of a carbon body as a contact material for vibratorily moving the carbon particles in the cell. Vibrating carbon plates for actuation of microphone carbon contacts have been long known, and are widely employed in ordinary microphone transmitters. As used till now the carbon plate portion acting on the carbon contacts was only a part of a larger carbon plate, clamped at the edges, and serving as the vibratory diaphragm and imparting the sound vibrations to the portion acting on the carbon granules. In ordinary microphones there was no difliculty in using the carbon plates for dual function because there the diaphragn'l isnormally not under pull, and the only tension to which it is subjected is that due to phragms are applied to microphone amplifiers,

they either crack soon because of the excessive magnetic pull, or they must be left under such light pull that they are not able to transmit enough power to the cell filling. I

Microphone amplifiers also came into use in which a round diaphragm of thin stretched metal foil, only a few mils thick, coated with gold, was used to hold and impart movements to the carbon grains in the microphone chamber. It was found, however, that the carbon grains in the cell deposited a smudgy mass on the contacting metal surface, forming thereon resistance compositions notwithstanding the precious metal coating, and that the amplifier would as a result deteriorate after a short time, making it useless. The microphone amplifier of the invention overcomes the ,difliculties encountered with allcarbon diaphragms as well as those encountered with all-metal diaphragms. In the improved amplifier the contact plate acting on the carbon particles in the cell is only large enough to extend beyond the edges of the cell and vibrate ,the carbon balls thereon without permitting their :falling out. This carbon plate, with the portion of the diaphragm strip to .which itis attached, and the small armature underlying .the latter, constitute a rigid, fiat unit which performs a substantially purely translational piston-like movement when impelled toward, and pulled from, the chamber opening. As a result, substantially the entire ball body receives a uniform impact, and accordingly undergoes a relatively uniform resistance variation in the circuit which conveys through it the current to the receiver. This uniform resistance variation, distributed over almost the entire depth of the carbon body having uniform contact surfaces, secures a high intensity of sound reproduction, and thus. supplies the chief requirement of the amplifier.

Because of the abilityto produm this uniform resistance variation, while using a great quantity of small contact surfaces, there is also obtained a very high quality of sound production, thus combining intensity and quality of reproduction to a very high degree, which heretofore seemed difficult to reach.

The combined use of a carbon plate contact member with a resilient metal diaphragm secures all the benefits of metallic material for taking care of the stresses impressed upon the diaphragm by the magnetic system in impartingit the vibrations. This diaphragm may be made from a thin resilient supporting sheet, of metal or other material of high tensile strength, such as mica, having attached to one side of its center a carbon plate of a size sufiicient to cover the chamber opening and vibrate the carbon-grains, and to the opposite side of its center an armature disk, the three elements forming a fiat, rigid center unit with a resilient sheet extending around it. This resilient sheet may be of circular form and either of sufficient thickness and held clamped at the edges; or of thin foil and held stretched at the edges, for vibrating the center unit.

A simple and very desirablediaphragm unit, and one easiest to adjust, is obtained by following the construction shown in Figs. 2 to 6, and using for the diaphragm an elongated, relatively narrow, fiat strip of resilient metal, or other sheet material of high tensile strength, such as mica. At the center, the strip is provided with a suitably shaped supporting portion holding attached to it on one side the microphone carbon plate and on the other side the armature. From both sides of this rigid center portion extend the resilient, relatively narrow, strip portions which are clamped at their ends to maintain the carbon plate in the proper position before the microphone chamber opening and the armature before the magnet pole faces, to permit vibration within the narrow space therebetween.

The strip shape of .the diaphragm unit permits very easy adjustment of resonant frequency of the diaphragm and of the widthof the gaps by merely slightly loosening the screws holdingthe clamping blocks 64. Then the adjusting blocks 63 supporting and pivoting the strip at their inner edges are slightly pushed inwardly or outwardly until the desired adjustment is obtained and the screws then tightened By such movement of the adjustment blocks 63-, the gaps may be adjusted with an accuracy of less than /10,000". Instead of clamping the diaphragmstrip ends. they may beheld stretched in suitablestretchers mounted on the magnet structure, and the tension of the diaphragm adjusted by controlling the stretching.

High and substantially uniform response over the sound frequency range is obtained by making the diaphragm resonant between 1,500 and atom cycles per second, a frequency from the range between 1,800 and 2,200 cycles being preferred; and at the same time making the impedance of the actuating coil equal to the impedance of its input circuit at a frequency between IlflO and 400 cycles, and preferably near 200 cycles.

Another feature of the invention resides in the special coordination of the elements of the electi'omagnet and the microphone to secure an eilicient, high quality power transformation in the amplifier unit, and yet make its mounting and wear, firm, comfortable and inconspicuous, By the powerful magnetic action and symmetrical excitation of the armature gap is obtained a symmetrical low magnet core arrangement that forms an elongated structure extending lengthwise the elongated strip diaphragm.

The complete microphone amplifier is constructed as a low and narrow unit fitting over the top of the dry cell battery with'which the device is used, as shown in Figs. 7 and 8, the bottom having battery plug pins fitting into the conventional battery socket sleeve terminals provided on the top'surface of the battery The lower 1 the amplifier unit is, the less it is likely to be tipped over, or pulled out of its place, or have its plugs broken and thus damaged, and its functioning interfered with. The design of themechanical elements of the amplifier as a unit formed around a narrow diaphragm strip, makes it possible to cut down the total height of the unit practically to the width of the pole plate. The microphone chamber lies in vertical direction, giving the proper distribution of the carbon ball pressure on the contact walls of the chamber and the instrument is automatically maintained in the most favorable operating position. The

several elements of the magnetic system are mounted on one side of the pole plate with a minimum of manipulations, and on assembly constitute a unit complete by itself. The diaphragm and the microphone chamber are assembled as a separate unit on. the other side of the pole plate, and the electrical and mechanical structure of the amplifier are completed and adjusted before insertion into the casing. The mounting. of the assembled structure within the casing requires merely its insertion within the opening of thecasing. The spring contacts from the plugs and sockets on the walls of the casing automaticallyestablish the conducting connections with the contact terminals on the structure, and no soldering of connections or involved manipulations are necessary after insertion.

To connect the transmitter andreceiver with the amplifier and the battery, a set of three contact sleeves is provided in one of. the lateral .end walls of the amplifier casing into which the threepin plug of the cord is inserted. This plug forms a longitudinal extension of the amplifier casing and lies on the top of the battery. This mounting of the plug on the lateralv end of the amplifier casing keeps the height of .the elements projecting above the battery down. The force of the plug does not act additively to the tilting force of the amplifier unit, but in a different direction where it is not cumulative.

The amplifier hearing-aid'device as shown-in the drawings may be readily turned into a nonamplifying single-circuit aid by simply pulling out the cordplug 104 from the amplifier, pulling out the amplifier 15 with its plugs 108, 111. from and pin a engages the battery fflie'battery, and plugging in the cord plug 104 into the battery, the plug pins being polarized so that pin 101 engages the battery 'aIeeve terminal engaged by amplifier pin 108, sleeve terminal .flnlaled by amplifier pin 111. A single direct operating circuit is then obtained as follows: the right hand battery socket through its eat with plug pin 103 of the cord plug,

s, tact "in its connecting strand in cord 14 to receiver coil thence t pin of the transmitter plug 3'1, 2'1, movable contact 30, contact 28, the two microphones 21, 22, plug conplug pin 36, cord 14, cord plug pin 101 to theother battery pole.

1 "Cuba single cord is used both for single-ciredit or cascade-amplifier operation, and the plug connections are simple and do not require parcare and attention in handling. In order s the central pin 102 of cord plug 10% when, directly into the battery, the terv'mav be provided with a third dead pin hole 118 its two terminal sleeves; or'an ,fidaptor may'be provided which has two pins the battery and three sockets, two externalliveones' connected to the'two battery done de'ad one'for receiving the central dtgd 1 111 of the plug; or the central pin 102 of the cord plug my be shorter. or self-retractin the two end pinswill engage the battery *5 the intensity,

terminal sleeves without being interfered with by ,the'c'entral pin. 3

The control imit provided on the transmitter enablm cutting out of the battery and control of whether the hearing-aid device is with the ainplifier or without the amplifier, circuit arrangement being such that when used with an amplifier, theresistor lies in the receiver circuit and'the stationary contact member of the control unit lies in the circuit of the primary microphone, and that when used without the amplifier, the resistor and the stationary contactmember are connected in series between the receiver and the primary microphone.

15 The amplifying hearing-aid of the present inven'tion embodies thus a number of important fatureswhich add greatly ,to its efiiclency and tiitnity as a hearing-aid. The use of a carbon (plate covering only the opening of the carbon gomoldingchamber and rigidly supported on one side of a higlr-tensile-strength vibratory sheet 'fdiaphra'g n, carrying on the opposite side a mag- ;netically,'vibrated armature, enables the combiof; the benefits of the use of carbon as the :top theiiatfery, with small on 5 oscillation imparting contact wall with the benefits ofth'e still metal sheet for the vibrator action. The useof very small carbon balls as chamgives h gh intensity as'wpll as high of sound reproduction. Formation of the eet diaphragm as a strip and longitudinally fadjustable clamping of its ends, enables easy and laccurate adjustment of the gaps, and the read- 'nagnt frequency of the diaphragm. The die.-

'pnragmwith a high resonance frequency around fet "150 1.5 2200 cycles per-second and the actuatin equal the impedance of fits input circuit at around 200 cycles per second,

- a'fhigli and substantially uniform response over the'entire frequency range, important for w microphone amplifier aids. Forminga symmetelectromagnetic system and microphonechamber into alow, elongated struc-- plan; the narrow long diaphragm gives all qvgi but amplifier unit, nesting on the equivalents thereof will suggest themselves to those skilled in the art. It is, accordingly, de-

sired that the appended claims be given a broad construction commensurate with the scope of the invention.

We claim as om invention: V

1. A portable microphone amplifier for amplifying electrical sound-frequency current oscillations in a portable hearing-aid device, comprising a microphone chamber having an insulating surrounding wall with an exposed opening on one side thereof, a terminal contact member bounding the surface of said chamber on the side opposite said opening, a relatively rigid carbon block having a surface covering said opening, a filling of carbon grains in said chamber extending between said contact member and said carbon black and constituting a variable resistor therebetween, a resilient thin sheet of material having substantially higher tensile strength than said carbon block underlying said block and having free flexible portions extending beyond the opposite edges of said block to constitute a vibratcry diaphragm unit for imparting to said block a vibratory movement toward andaway from said contact member and vary the pressure exerted on said filling substantially uniformly over the major portion of the cross sectional area of said chamber, said block having an edge portion sealing said opening and retaining said filling withthe amplified oscillations to a receiver in a portable hearing-aid device, comprising a substantially fiat microphone chamber having an insulating surrounding wall with an exposed opening on one fiat side thereof, a terminal contact member opposite said opening, a relatively rigid carbon plate covering said opening, a filling of carbon balls in said chamber extending, between said contact member and said carbon-plate and constituting' a variable resistor therebetween, a resilient thin sheet of material having substantially higher tensile strength than said carbon plate underlying saidplate and having free flexible portions extending beyond the opposite edges of said plate to constitute a vibratory diaphragm unit for imparting to said plate a vibratory movement toward and away from said contact member and vary the pressm'e exerted on said filling substantially uniformly over the major portionof the cross sectignalQarea of said chamber, said plate having'an edge portion sealing said opening and retaining said filling within said chamber during said movement, a magnetic armature secured to said sheet opposite said plate and constituting with said plate and the intermediate sheet portion a rigid fiat member, and electromagnetic -means on the bounding the surface of said chamber on the side side of said armatin'e opposite said sheet actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

3. A portable microphone amplifier for amplilying electrical sound-frequency current oscillations received from a microphone and supplying the amplified oscillations to a receiver in apertable hearing-aid device, comprising a substantially flat microphone chamber having an insulating surrounding wall with an exposed opening on one fiat side thereof, a terminal contact member bounding the surface of said chamber on the side opposite said opening, a relatively rigid carbon.

plate covering said opening, a filling ofcarbon balls in said chamber extending between said contact member and said carbon plate and constituting a variable resistor therebetween, a resilient thin metallic strip underlying said plate and having free flexible portions extending beyond the opposite edges of said plate and clamped at the ends to constitute a vibratory diaphragm unit for imparting to said plate a vibratory movement toward and away from said contact member and vary the pressure exerted on said filling substantially uniformly over the major portion of the cross sectional area of said chamber, saidplate having an edge portion sealing said opening and retaining said filling within said chamber during said movement, a magnetic armature secured to said sheet opposite said plate and constituting with said plate and the intermediate sheet portion a rigid flat member, and electromagnetic means on the side of said armature opposite said sheet actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

4. A portable microphone amplifier for amplifying electrical sound-frequency current oscillations received from a microphone and supplying the amplified oscillations to a receiver in a portable hearing-aid device, comprising a substantially fiat microphone casing having a closed insulating border wall confining a flat cell having an opening of the width of said cell on one flat side thereof, a terminal contact member bounding the surface of said cell on theside opposite said opening,.a relatively rigid carbon plate covering said opening, a filling of carbon balls in said chamber extending between said contact member and said carbon plate and constituting a variable resistor therebetween, and a resilient thin narrow metallic strip underlying said plate and having free flexible portions extending beyond the opposite edges of said plate and clamped at the ends to constitute a vibratory diaphragm unit for imparting to said plate a vibratory movement toward and away from said contact member and vary the pressure exerted on said filling substantially uniformly over the major portion of the cross sectional area of said cell, said plate having an edge portion sealing said opening and retaining said filling within said cell during said movement, a magnetic armature secured to said strip oppositersaid plate and constituting therewith a rigid flat member, and electromagnetic means on the side of said armature opposite said strip actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

5. A portable microphone amplifier for amplifying electrical sound-frequency current oscillations received from a microphone and supplying the amplified oscillations to areceiver in a portable hearing-aid device, comprising a microphone casing having a closed'insulating border wall-confining a flat cell having an opening-on one side thereof, a terminal contact member bounding the surface of said cell on theside opposite said opening, a relatively rigid carbon plate covering said opening, a filling of carbon ballsof a diameter not greater than 0.7 millimeters in said cell extending between said contact member and said carbon plate and constituting a variable resistor therebetween, a resilient thin sheet of material having substantially higher tensile strength than said carbon plate underlying said plate and having free flexible portions extending beyond the opposite edges of said plate and clamped at vthe ends to constitute a vibratory diaphragm unit for imparting to said plate a vibratoryn ovement toward and away from said contact member and vary the pressure exerted on said filling substantially uniformly over the major portion of the cross sectional area of said cell, said plate having an edge portion sealing said opening and retaining said filling within said cell during said movement, a magnetic armature secured to said sheet opposite said plate and constituting with said plate and the intermediate sheet portion a rigid flatmember, and electro-magnetic means on the side of said armature opposite said sheet actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

6. A portable microphone amplifier for amplifying-electrical sound-frequency current oscillations received from a microphone and supplying the amplified oscillations to a receiver in a portable hearing-aid device, comprising a microphone casing having a closed insulating border wall confining a flat cell having an opening on one side thereof, a terminal contact member bounding the surface of said cell on the side opposite said opening, a relatively rigid carbon plate covering said opening, a filling of carbon balls in said cell extending between said contact member and said carbon block and constituting a variable resistor therebetween, a resilient thin narrow metallic strip-supporting said plate at said cell opening to hold said balls in said cell and vary the resistance of said balls upon being vibratorily moved toward and away from said contact member, said plate having an edge portion sealing said opening and retaining said filling within said cell during said movement, a magnetic armature secured to said strip on the side opposite to said plate and constituting with said plate and intermediate strip portions a rigid flat central member, said strip extending beyond the edges of said plate and armature to constitute therewith a vibratory diaphragm unit having its effective resilience inthe portions outside of said plate, means for clamping opposite ends of said diaphragm strip at adjustably variable distances from said central member, and electromagneticmeans on the side of said armature opposite said sheet actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

'7. A portable microphone amplifier for use in conjunction with a portable hearing-aid device having an input circuit impressing weak electri cal sound-frequency oscillations on said amplifier and an output circuit supplied with amplified oscillations by said amplifier, comprising a m crophone casing having a closed insulating border wall confining a fiat cell having an opening on one side thereof, a. terminal contact member bounding the surface of said cell on the side opposite said opening, a relatively rigid carbon plate covering said opening, a filling oi'carbon balls in said extending between said contact memben'and said carbon block andconstituting a variable resistor therebctween, a resilient thin sheet of material having substantially higher tensile, strength than said carbon plate underlying said plate and conflict member and vary the pressure exerted,

having free flexible portions extending beyond the opposite edges of said plate to constitute a vibratory forimparting to said plate a vibratory movement toward'and away tromrsaid on said filling substantially uniformly over the 'maior portion of the cross sectional area of said cell, saladplate having an edge portion said openirigand retaining said filling within said cell e 'during'said movement, a magnetic armature securedto' said sheet opposite said plate and constituting with said plate and the intermediate sheet portion a vibratory diaphragm unit having a rigid center member and effective resilience in 180 the border poitions outside said rigid member, a

relement to ca magnetic core body having pole surfaces spaced by ja'srnall gap from said armature and consti- -tuting 'a low reluctmceinduced flux path forcing a fiermancnt flux through said gap, and an actu- --ating coil interlinked :with said core body and connected to said input circuit to induce flux in said gap imparting vibrations to said diaphragm and varying accordingly the resistance of the filling in said cell, said diaphragm unit'having' a resonance frequency lying within the range between 1500 and 2500' cycles per second and said actuating coil having an impedance of the order of the impedance of the input circuit at a current frequency within the range between 100 and 400 cycles per second. 8. An inconspicuous portable microphone ampliilerfor detachable mounting on the top of an inconspicuous portable flat dry battery casing of a portable hearing-aid device including a transmitter energized by said battery, comprising a microphone casing having a closed insulating border wall confining a fiat cell having an opening on one side thereof, a terminal contact member bounding the surface of said cell on the side opposite said opening, a relatively rigid carbon plate-covering said opening, a resilient thin narrow ir'lctallicstrip underlying said plate and having free flexible portions extending beyond the 'op'pomte edgeszof said plate and clamped at theen'dsto constitute a vibratory diaphragm unit for imparting to saidplate a vibratory movement toward and away from said contact memher and vary the pressure exerted on saidfilling substantially uniformly over the major portion of the cross sectional area of said cell, said plate having an edge portion sealing said opening and retaining said filling within said cell during said t, a magnetic armature secured to said strip opposite said plate and constituting with said plate and the intermediate strip portion a substantiallr it fl flat member, an elongated magnetic core having coreelements extending along said diaphngmstrip on the side opposite said casing and corstituting a low reluctance induced concentric pole faces of oppopolarltysymmetrically positioned against a shortigap from said-armature, 9 mfing coil oscillations n with said core flux fluctuations in said gap vibrations to;said diaphragm unit and therettuuughto said carbon balls, and an elongated casing enciosing said amplifier elements having a relatively low height and a Length equal to M twice theheight and ,holding said flat ing plug pins leading to'theiexternal circuits of I said hearing-aid.

9. A portable microphone amplifier for amplifying electrical sound-frequency current oscillations in a portable hearing-aididevice, comprising a microphone chamber havingan insulating surrounding wall with an exposed opening on one in said chamber extending between said contact member and said carbon block and constituting a variable resistor therebetween, a resilient thin sheet of material having substantially higher I tensile strength than said carbon block supporting said block at-said: opening to hold said grains in said chamber, means constituting a magnetic armature on the side of said sheet opposite said block, said sheet extending beyond the edges of said block and constituting therewith a vibratory diaphragm unit having its effective resilience in .the portions of said sheet outside said block for imparting to said block a vibratory movement toward and away from said contact member uniform over the major portion of the cross-sectional area of said chamber, said block having an edge portion sealing said opening and retaining said filling within said chamber during said movement, and electromagnetic means on the side of said armature opposite said sheet actuated by supplied current oscillations to impart said vibratory movement to said diaphragm unit.

10. 'An inconspicuous portable microphone amplifier for detachable mounting on the top of an inconspicuous portable fiat dry battery casingof a portable hearing-aid deviceincluding a transmitter energized by saidbattery, comprising a microphone casing having a I closed insulating border wall confining a flatcell having an opening on one sidethereof, a terminal contact member bounding the surface of said cell on the side opposite said opening, a carbon plate covering said opening, a filling of carbon grains in said cell extending between said contact member and said carbon plate, an electromagnetic mechanism for imparting a vibratory movement to said carbon plate toward and away from said contact member and vary the resistance of said granule filling, and an elongated casin enclosing said amplifler elements having arelatively low height and a length equal to about twice the height and holding said flatmicrophone cellin upright position, the bottomside of saidamplifler casing fitting within the area oi-said battery casing top and having downwardly extending plug. pins. engaging the battery sleeves to establish the connectionsfrom-the battery to the elements in theinterior of said casing, one of the end surfaces of the elongated casing carrying contact meansior establishing a plug pin engagement with the external circuits of said hearingaid, the contact surfaces of said engagement extending in the direction of the length of said casmgt Tl 1 An inconspicuous portable microphone amplifier for detachable mounting on the top of an inconspicuous portable fiat dry battery casing of a portable hearing-aid device including a transmitter and receiver energized by said battery to be worn on the body of the user, comprising a microphone casing having a closed insulating border wall confining a fiat cell having an opening on one side thereof, a terminal contact member bounding the surface of said cell on the side opposite said opening, a vibrating member having a surface covering said opening, a filling of carbon grains in said cell extending between said contact member and said vibrating member, an electromagnetic mechanism for imparting a vibratory movement to said vibrating member toward and away from said contact member and varying the resistance of said grain filling, and an elongated casing enclosing said amplifier elements having a relatively low height and a length equal to about twice the height and holding said flat microphone cell in upright position, the bottom side of said amplifier casing fitting within the area of said battery casing top and having plug pins detachably engaging battery terminal sleeves in said battery top to establish circuit connections from the battery to elements in the interior of said casing, and additional contact means on one of the end surfaces of the elongated casing for establishing a detachable plug pin engagement with an external plug member holding terminal contacts of external circuit leads of said hearing-aid connected by said plug pin engagement to elements in the interior of said casing, the plug pins between said casing and said battery extending downwardly into the battery terminal sleeves and the plug pin engagement between the end surface of said casing and said external plug extending in the direction of the length of the casing holding the battery, the amplifier casing and external plug member joined into a stable self-supporting unit resistant to external forces tending to loosen the Junctions therebetween.

12. An inconspicous portable microphone amplifier for detachable mounting on the top of an inconspicuous portable flat dry battery casing of a portable hearing-aid device including a transmitter and receiver energized by said battery to be wornon the body of the user, comprising a microphone casing having a closed insulating border wall confining a fiat cell having an opening on one side thereof, a terminal contact member bounding the surface of said cell on the side opposite said opening, a movable contact member having a surface covering said opening, a filling of carbon grains in said cell extending between said terminal contact member and said movable contact member, an electromagnetic mechanism for imparting a vibratory movement to said movable contact member toward and away from said terminal contact member and varying the resistance of said grain filling, and an elongated casing enclosing said amplifier elements having a relatively low height and a length equal to about twice the height and holding said flat microphone cell in upright position, the bottom side of said amplifier casing fitting within the area of said battery casing top and having downwardly extending plug pins engaging the battery terminal sleeves to establish the circuit connections from the battery to the elements in the interior of said casing, one of the end surfaces of the elongated casing carrying contact means for establishing a plug pin engagement with the external circuits of said hearing-aid, the contact surfaces of said engagement extending in the direction of the length of said casing.

HUGO LIEBER. EMMANUEL CHRIST NICHOLIDES. 

